E. L. Troxell — Helaletes Redefined. 365 



Aet. XXXV. — Helaletes Redefined; by Edward L. 



Teoxell. 



[Contributions from, the Othniel Charles Marsh Publication Fund, Pea- 

 body Museum, Yale University, New Haven, Conn.] 



The genus Helaletes Marsh constitutes a group of the 

 smallest of the tapiroids. For two reasons I am 

 prompted to redescribe this important genus : first, 

 because it is very much misunderstood, and has no pub- 

 lished drawings ; and second, because some new features 

 have come to my attention which Marsh himself had 

 not noted. 



The species Lophiodon nanus Marsh was the first one 

 described; the holotype consists of both maxillaries. 

 Helaletes hoops, however, is the genoholotype and is 

 based on the greater part of the skull, jaws, and skeleton 

 of one individual. Whether or not other existing species 

 should be assigned to this genus is uncertain; two have 

 been referred to it, perhaps with doubtful justification. 

 These are Dilophodon minusculus Scott and Desmato- 

 therium guyoti Scott. 1 



Dilophodon minusculus Scott is shown to have no pos- 

 terior heel on M 3 and is therefore quite different from H. 

 hoops. Only its small size and the absence of F 1 separate 

 it from Hyrachyus, but these may be sufficient for a sub- 

 genus at least. 



Desmat other ium guyoti, which has been referred to 

 Helaletes by authors, differs from H. hoops in its much 

 greater size, in the relatively greater M 3 and in the dis- 

 proportion between the large molars and the premolars. 

 On the other hand, the partial separation of the internal 

 cusps on the third and fourth premolars and the diastema 

 in front of C 1 , likewise the general resemblance in the 

 form of the molars, indicate relationship, but Desmato- 

 therium should retain at least subgeneric distinction. 



Hyrachyus nanus Leidy is frequently referred to Hela- 

 letes by writers who seem to be unaware of the species 

 Helaletes nanus (Marsh) which precedes. Scott has 

 referred Leidy 's species to his genus Dilophodon because 

 of the bilobed M 3 and the absence of P 2 ; if this is a cor- 



1 W. B. Scott, Contrib. from E. M. Mus. Geol. & Arch., Princeton Coll., 

 Bull. 3, 46-53, pi. 8, 1883. ' 



